It is well-established in the chemical literature that aryl halides react with alkenes under the influence of palladium catalysts to form vinylically substituted products. In general, these reactions are performed using aryl bromides as the source of the aryl moiety since bromides are substantially more economical than the corresponding iodides. For example, Patel et al., J. Orc. Chem., 42(24):3903 (1977), describes palladium-catalyzed vinylic substitution reactions with carboxylic acid derivatives. Bromobenzoic acids are reacted with vinylic compounds in the presence of triethylamine with palladium acetate and tri-o-tolylphosphine as the catalyst. Unfortunately, the bromides do not react as fast and clean as the iodides, making reactions using iodides more attractive than those using bromides. Iodides, however, have been considered too expensive for most applications.
These reactions generally are performed using soluble, homogeneous organopalladium species, usually beginning with palladium acetate, Pd(OAc).sub.2. In one literature article, Bull, Chem. Soc. Japan, 46:1505-1508 (1973), it is mentioned that palladium black can be used effectively. In this article, methanol is used as the reaction solvent at a reaction temperature of 120-125.degree. C. Because of these harsh conditions, use of this method results in the undesirable necessity of using pressure vessels, which detracts from the practical utility of the method.
Heck et al., J. Orq. Chem., 37(14):2320 (1972), describes palladium-catalyzed vinylic hydrogen substitution reactions with aryl, benzyl, and styryl halides. One of the reactions tried by Heck was the reaction of 4-iodoanisole with methylacrylate in the presence of a palladium catalyst to form methyl-p-methoxycinnamate. The preferred palladium catalyst was an in situ palladium acetate reduction catalyst. The yield for this reaction was a rather low 68%. Further, the use of the homogeneous palladium catalyst is expensive since these catalysts are not easily recovered and rejuvenated for further use. Although the Heck article states that a palladium on carbon catalyst may be used, the authors state that these reactions are slower and the yields lower than with the homogeneous catalysts.
Thus, there is a need in the art for an economical method for producing high yields of cinnamates. Further, there is a need for a process which utilizes a catalyst which can be easily recovered and inexpensively used.